Breathing new life into monitoring devices

Metabolic waste could in the future power wearable or implantable electronics. The AMI BioPhysics group has developed a prototype device that is fueled by carbon dioxide from a person’s breath and can provide enough energy to power a light-emitting diode.  

Wearable and implantable technologies are redefining how we exchange information, receive entertainment, and monitor health and fitness. Although traditional batteries can be used to power these electronics, their limited lifetime and lack of biocompatibility are not ideal for powering devices that interface with the human body. The ongoing integration of this technology into living organisms thus requires new power sources and countless implantable devices such as heart pacemakers, sensors, drug delivery pumps, or prosthetics would benefit from self-charging power systems. The possibility to generate electricity inside the body would eliminate the need for replacement surgery, however minor, and could also provide sustained power for wearable devices such as electrically active contact lenses with an integrated display.

Biomedical devices that harvest energy from human metabolites are already under development, for example in the form of implantable chips that can monitor diabetes patients’ blood sugar levels by oxidizing glucose. Another approach for monitoring is to explore novel power sources that can be fueled by the activity of the wearer. Without needing to be “plugged in”, these sources could integrate seamlessly into daily life.

The AMI researchers investigated the development of a sustainable process to recharge a bio-inspired battery, using carbon dioxide (CO2) from a person’s breath.  To demonstrate this concept, the researchers developed a prototype device based upon reverse electrodialysis. This method is already used to harvest energy from waters having different salt concentration, such as seawater and freshwater, and exploits the ion gradient between them. The AMI researchers exploited that such ion gradients can also be generated by dissolving CO2 in water and demonstrated that the electrical power that can be generated is sufficient to drive small electronic devices, such as a light-emitting diode.

“This work is about using a metabolic waste product in conjunction with ion-gradient-based power generation to develop a wearable or implantable power source that could potentially be recharged indefinitely,” explains the AMI BioPhysics chair Prof. Michael Mayer. “This is one more step towards having a battery that never needs to be plugged in, recharging passively, relying on ion transport rather than on chemical reactions to make it happen.”  

The research should benefit another of the group’s ongoing projects funded by the European Union’s Pathfinder program called INTEGRATE, which aims to build and power artificial muscles.  “The ability to convert metabolic energy for powering artificial muscles would be another step towards the enhanced integration of prostheses into the human body” says Alessandro Ianiro, a group leader in the BioPhysics group, who heads the INTEGRATE project.

The AMI researchers were originally inspired by the electric eel, before pivoting to the electric organ of the torpedo ray. To create their devices, they developed a hybrid material by infusing paper with an ion-conducting hydrogel. This allowed them to create, organize, and reconfigure stacks of thin, arbitrarily large gel films with differences in salt concentration. Their project demonstrated that the biological mechanism of generating significant electrical power is possible with benign and soft materials in a portable size.  The next challenge is to improve the longevity and robustness of these “body batteries”.

Reference: Kalkus, T. J.; Guha, A.; Scholten, P. B. V.; Nagornii, D.; Coskun, A.; Ianiro, A.; Mayer, M. The Green Lean Amine Machine: Harvesting Electric Power While Capturing Carbon Dioxide from Breath. Advanced Science, 2021, 2100995.